1. Field of the Invention
This invention relates to a radiation shielding grid for use with a radiation detection panel comprising a plurality of spaced discreet radiation sensing elements, and more particularly to a method for designing such a grid to eliminate Moirxc3xa9 patterns and to the resulting grid.
2.Description of Related Art
Direct radiographic imaging using panels comprising a two dimensional array of minute sensors to capture a radiation generated image is well known in the art. The radiation is image-wise modulated as it passes through an object having varying radiation absorption areas. Information representing an image is captured as a charge distribution stored in a plurality of charge storage capacitors in individual sensors arrayed in a two dimensional matrix.
X-ray images are decreased in contrast by X-rays scattered from objects being imaged. Anti-scatter grids have long been used (Gustov Bucky, U.S. Pat. No. 1,164,987 issued 1915) to absorb the scattered X-rays while passing the primary X-rays. Whenever the X-ray detection panel resolution is comparable or higher than the spacing of the grid, an image artifact from the grid may be seen. Bucky also taught moving the anti-scatter grid to eliminate that image artifact by blurring the image of the anti-scatter grid (but not of the object, of course). The anti-scatter grid may be linear or crossed. Bucky furthermore taught a focused anti-scatter grid.
Improvements to the construction of anti-scatter grids have reduced the need to move the grid, thereby simplifying the apparatus and timing between the anti-scatter grid motion and X-ray generator. However, Moirxc3xa9 pattern artifacts can be introduced when films from such apparatus are digitized. Image intensifiers for fluoroscopy can also produce Moirxc3xa9 pattern artifacts. It is known and recommended to align the bars of a linear anti-scatter grid perpendicular to the direction of scan (The Essential Physics of Medical Imaging, Jerrold T Bushberg, J. Anthony Seibert, Edwin M. Leidholdt,Jr., and John M. Boone. c1994 Williams and Wilkins, Baltimore, pg. 162 ff.).
When the X-ray detection panel is composed of a two dimensional array of picture elements or X-ray sensors, as opposed to film or raster scanned screens, the beat between the spatial frequency of the sensitive areas and that of the anti-scatter grid gives rise to an interference pattern having a low spatial frequency, i.e. a Moirxc3xa9 pattern. U.S. Pat. No. 5,666,395 issued to Tsukamoto et al. teaches Moirxc3xa9 pattern prevention with a static linear grid having a grid pitch that is an integer fraction of the sensitive area pitch.
Two cases are discussed in the aforementioned patent. In the first, the sensors are positioned in the array so that there is no dead space between sensor elements. In this instance, the grid pitch is made equal to an integer fraction of the sensor pitch, the distance between adjacent sensor centers. In the second case, the sensors are separated by dead spaces, i.e. interstitial spaces which are insensitive to radiation detection. In this case, the grid pitch is made to correspond to the sensor pitch and is held in a steady position relative to the detection panel such that the grid elements are substantially centered over the interstitial spaces.
One difficulty with the above mentioned cases is that construction of a radiation detection panel having no interstitial spaces between adjacent sensor elements is technically problematic. When there are interstitial spaces present, maintaining the anti-scatter grid in a fixed position relative to the radiation sensor array is often impractical.
There is thus still a need for a grid that will shield from incident scattered radiation an X-ray radiation sensor array comprised of discreet non contiguous elements separated by non-radiation sensitive interstitial spaces that does not require accurate fixed positioning relative to the radiation detection panel, or, in the alternative, does not require moving the grid during exposure to avoid creating Moirxc3xa9 patterns. There is a need for a grid that avoids creating Moirxc3xa9 patterns despite mismatch between the grid and the detection panel.
According to this invention there is provided a scattered radiation shielding grid comprising a plurality of tiles, each tile being a replicate of a prototile, each prototile comprising a radiation absorbing material arranged in a motif, the motif of radiation absorbing material comprising a plurality of non-overlapping linear segments of radiation absorbing material, wherein the linear segments have equal lengths. The motif may be a pinwheel motif.
Each prototile comprises a width W(p) and a length. The motif is contained solely within the prototile. The prototile width W(p)=W/(Ixc2x1Mxe2x97xafI) and W(p)xe2x89xa0W+D. W is the radiation sensitive area width of a radiation detection panel comprising a plurality of equal size radiation sensors separated by interstitial spaces having a width D, over which the grid is positioned, I is an integer and M is a non-integer.
Furthermore, the invention provides a scattered radiation shielding grid comprising a radiation absorbing material, and a radiation detection panel over which the grid is positioned. The radiation detection panel comprises a plurality of equal size radiation sensors having a radiation sensitive area width W, separated by radiation insensitive interstitial spaces having a width D. The grid radiation absorbing material forms a pattern through a combination of a plurality of substantially identical tiles, each tile being a replicate of a prototile. Each prototile in turn comprises: a width W(p)=W/I, wherein I is an integer; a length; and a pinwheel motif of the radiation absorbing material contained solely within the prototile.
Further provided by the present invention is a method for designing a pattern for absorption material for a scattered radiation shielding grid for a radiation detection panel comprising an array of a plurality of sensors each having a radiation sensitive area having a width W and a length, wherein the sensors are arrayed so that each radiation sensitive area is separated by each adjacent radiation sensitive area by an interstitial space having a width D. This method comprises:
a) determining a sensor width W corresponding to the width of the radiation sensitive area of the sensor;
b) creating a prototile having a width W(p)=W/I wherein I is an integer;
c) producing within the prototile a pinwheel motif of the radiation absorbing material; and
d) tiling a plurality of tiles, each being a replicate of the prototile to produce the pattern, the pattern comprising a combination of the pinwheel motif of the tiled tiles.
Also provided is a method for designing a scattered radiation shielding grid comprising a pattern of radiation absorbing material for a radiation detection panel comprising an array of a plurality of sensors each having a radiation sensitive area having a width W and a length, wherein the sensors are arrayed so that each radiation sensitive area is separated by each adjacent radiation sensitive area by an interstitial space having a width D, the method comprising:
a) determining a sensor width W corresponding to the width of the radiation sensitive area of the sensor;
b) creating a prototile having a width W(p)=W/(Ixc2x10.10I), W(p)xe2x89xa0W+D and wherein I is an integer;
C) producing within the prototile a pinwheel motif of radiation absorbing material; and
d) tiling a plurality of tiles, each being a replicate of the prototile to produce a pattern comprising a combination of the pinwheel motifs of the tiled tiles.
In another embodiment there is provided a method for generating a radiogram with an exposure system comprising radiation source, and a radiation detection panel. The radiation detection panel comprises an array of a plurality of sensors each having a radiation sensitive area having a width W and a length. The sensors are arrayed so that each radiation sensitive area is separated by each adjacent radiation sensitive area by an interstitial space having a width D. The method comprises positioning between the radiation source and the panel a grid comprising a radiation absorbing material formed in a pattern comprising a combination of a plurality of substantially identical tiled tiles, each tile being a replicate of a prototile, each prototile comprising a width W(p), a length and a pinwheel motif of the radiation absorbing material, the pinwheel motif contained solely within the prototile, wherein the prototile width W(p)=W/I where I is an integer.